The major objective of this subproject is to determine the effects of extracellular matrices on epithelial determination and differentiation into secretory ameloblast cells. Two distinct and relatively separate approaches will be attempted. First, the experimentalists will isolate an acellular extracellular matrix from developing incisor and molar tooth organs prior to ameloblast differentiation. This matrix will be used to ascertain the biological activity of separated mesenchymal and epithelial tissue from both oral and non-oral sources with regard to epithelial expression. In addition, it is proposed that efforts will be made to identify and characterize constituents of this extracellular matrix which possess "instructive information" involved in invoking epithelial expression. The second aim is to determine if dental papilla mesenchyme specifically regulates the pattern of extracellular matrix produced by ameloblasts in homologous and heterologous epithelial-mesenchymal tissue recombinants. These experiments rely on SEM as a major descriptive tool capable of delineating distinctive epithelial expressional patterns.